The present invention relates to a composition useful for forming glass fibers which possesses high alkali-resistance and are capable of being easily vitrified or fiberized.
In general, high alkali-resistance is required for glass fibers utilized for reinforcing cementitious products of a high alkali content, such as Portland cement and alumina cement, and alkali-resistant compositions having a variety of chemical compositions have been developed hitherto for manufacturing alkali-resistant glass fibers. For example, British Patent 1,290,528 discloses an alkali-resistant composition for forming glass fibers which contains a large amount of ZrO.sub.2. The alkali-resistant composition disclosed in this patent is excellent in alkali-resistance but is hardly vitrified. Moreover, this composition involves a problem, namely difficulty in fiberizing the composition into fibers because of its high spinning temperature. On the other hand an alkali-resistant composition disclosed in U.S. Pat. No. 3,861,925 which contains TiO.sub.2 and ZrO.sub.2 and is useful for forming glass fibers is easily fiberized because of its low spinning temperature but is not sufficiently high in alkali-resistance.
As a result of various research made to solve these problems, it has now been found that a composition for forming glass fibers possessing high alkali-resistance which can easily be vitrified and fiberized can be obtained by incorporating in a glass composition of SiO.sub.2 -ZrO.sub.2 -alkali metal oxide series at least one oxide of iron and/or oxide of copper.